Backrest of a chair



FIG. 1 is a front perspective view of a backrest of a chair;

FIG. 2 is a rear perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a right side view thereof, a left side view being a mirror image;

FIG. 6 is a top plan view thereof;

FIG. 7 is a bottom view thereof; and,

FIG. 8 is a partially enlarged view of area 80 in FIG. 3.

The broken line showing of the backrest of a chair is for the purpose of illustrating environmental structure and forms no part of the claimed design. 

CLAIM The ornamental design for a backrest of a chair, as shown and described. 